Does anyone know of the attitude of various games companies towards modding of their games? i.e. unfriendly vs neutral vs friendly?

The few I know about are:
Bethesda/ZeniMax/ID software (quite friendly in that they release mod tools for games like Oblivion, Fallout and Skyrim. Wish they had released all the official art tools for those games though)
Take 2/2K/Rockstar (generally mod-unfriendly as far as I am aware, I think the whole "hot coffee" thing for GTA made them nervous)
Activision Blizzard (with the exception of the StarCraft 2 tools and maybe some things for Call of Duty on PC, they seem to be not particularly mod friendly)
EA (some parts of EA like EA Sports seem to be mod-unfriendly, other parts used to be vaguely mod-friendly but are now at best neutral)
Valve (very mod friendly, probably one of the most mod friendly companies out there, releases basically full tools for their games)
Epic (they basically give away their entire engine for free and you only have to give them money if you want to make money yourself plus a lot of their games have had full mod support in the past and the new Unreal Tournament game will also have full mod support)

Anyone else got anything to add to this in terms of how friendly different companies are?

You forgot about indie game developers.
Torchlight is mod friendly to some extend. DoorKickers have mod support as you can make your own missions.
Can't say about others.
I asked Blackguards devs on the day Blackguards was released on gog about mod support of game they replied they will sure provide mod kit if more gamers get interested. But this never happened.

Activision Blizzard is a strange beast, they love drm but they encouraged fanmade content with warcraft 3 and starcraft ,while throwing out lawsuits when it come to their MMOs(for obvious reasons) and the diablos.

Lolwut? Warcraft 3 and it's editor pre-date the merger of Blizzard with Activision. Same with Starcraft 1.

Well, some time back I would have said Bethseda were one of the top companies promoting Modding. However recent developments, i.e. attempting to commercialise the modding domain has really degraded that opinion.

The other big player here is/was (not sure) Bioware. I.e. BG, IWD, NWN. The later of these, NWN, was built more as a set of tools with a story bashed on at the end. And the original BG games are probably among the most modded games ever.

Blizzard killed off the Diablo series with the latest release, hence zero respect there.

Torchlight (and 2, has a lot of modding, Synergies especially has had a lot of work put into it.

My final one would be M&B, this is probably the most modded game out there. Check out the forums, there are hundreds of total conversions over various time period scenarios etc. Prophesy of Pendor is probably the most well known, complete of the lot, but there are a lot of other really good ones and plenty of good ones still in the pipe.

If your interested, I would head on over to ModDB to start with, it is the best site for an overview of all games. Nexus is also great for ES, DA and various other ones. Taleworld forums for M&B. Spellhold Studios and Sorcerors Palace for BG, IWD. NWN Vault for NWN.

As a final note, some newer indie titles also having modding tools - Legend of Grimrock, Tales of Maj'Eyal etc. Really, there is far too much information to put into one post.

EA's The Sims series is more or less very modable and the developrs encourage the players to mod the game

oh ok. Activision should buy out Valve/Steam. assholes should stick together like a human centipede.

Like... This??

@rtcvb32 The human centipede is name of movie franchise.
Watch it at your own risk.
That movie is gross.

Yes i'm aware of that... heard it was awful... and gross... and i will never watch it, like i'll never watch two girls and <blank>

I would say the biggest hope regarding Bethesda is that the mod tools for Fallout 4 are as comprehensive as those for Fallout 3 and Fallout New Vegas. Heck, I want to see Bethesda go further and release a full set of art tools (I do wonder why they never released any art-making tools for Oblivion, Fallout 3, Fallout New Vegas or Skyrim given how moddable those games otherwise are)

Activision Blizzard did get things right eventually by releasing the art tools for Starcraft 2 but even they took a long time after the release of the rest of the mod tools before getting the art tools out there. I do wonder why in a number of cases art tools seem to never get released, take forever to get released or get released but are limited in what they can do compared to what the original devs used to build the game.

I think the Civ games are quite moddable so 2K isn't that bad.

In most cases art assets are not encoded in a format readable by Blender/Max/Maya/Gimp/whatever, so you need some extra tools to find, extract, and convert such assets so that they can be imported into your modeling/painting software of choice. Releasing the very same tools the devs worked with saves a lot of hassle to the modding community.
Blizzard like it fancy so they call them Art Tools, but usually they're just called scripts or plugins.

Ah, I see, Converters. Then I agree, these should be released with the modding tools.